LONDON — Millions of British voters go to the polls Thursday in the most important elections since David Cameron sealed a second term as prime minister a year ago — but this time it is Labour leader Jeremy Corbyn’s future that is at stake.

Despite the travails of the ruling Conservative Party, riven by internal squabbles over Europe, the local and regional elections are shaping up as the first real test of the Labour leader’s reign — and one that his opponents are desperate to ensure he fails.

Such is the animosity in the party, Corbyn’s inner circle now expect a leadership challenge to be launched by Labour MPs this summer following the elections, a senior ally of the Labour leader told POLITICO.

Labour expects losses across England and Wales in the “Super Thursday” election for mayors in London, Liverpool and Bristol, over 1,000 councillors in more than 100 English local authorities, plus two new MPs and 40 police and crime commissioners.

Corbyn’s closest aides have already begun preparations to fend off a co-ordinated attack by recalcitrant MPs. Senior sources say they could organize thousands of left-wing activists to staff phone banks “by the weekend” to fight any attempt to unseat him — and are confident they can see off any bid to replace him because of his continuing support among Labour members.

The concern is shared by Corbyn’s fiercest critics, who believe any bid to unseat him would fail and could even damage the party’s campaign against Brexit.

One senior Labour source, who insists it is “impossible to imagine Jeremy leading us into the next election,” said there was still no way to get rid of him in the short term: “There isn’t going to be a coup, that’s the reality. There will just be a lot of angry people talking shite on Friday.”

There is “no grand master plan” for getting rid of the leader, said a senior Labour MP. “It’s more like an ad-hoc resistance.”

Leadership challenge

If, as expected, Labour does not make gains, Corbyn will face angry MPs Monday during a private party meeting in the House of Commons. MPs confide that they expect to lose as many as 200 seats in English local government, with support dropping away even in the party’s heartlands.

Academics Colin Rallings and Michael Thrasher, experts on local elections, have forecast Labour losing 150 seats. Yet Labour MPs calculate the party needs to make at least 400 gains to show it has any serious chance of winning the next general election. No previous opposition has ever lost council seats at this point in the electoral cycle and gone on to win the general election.

Ed Miliband, the previous Labour leader, gained more than 800 councillors in 2012, the last time Thursday’s council seats were contested. Corbyn’s team insist this “high-water mark” makes it almost impossible to make any gains this time around.

A leaked list of Labour’s target councils given to the shadow cabinet exposes the limits of the party’s ambition.

“We will suffer some losses” — Source close to Jeremy Corbyn

Apart from the big prize of London, Labour is entirely focussed on defending councils the party currently controls rather than winning in new areas, the internal list seen by POLITICO reveals.

Overall, the party is focussing its fire on 16 key councils which it already controls.

The target seats are: Harlow and Norwich in the east of England; Derby, Lincoln Cannock Chase, Dudley and Redditch in the Midlands; Carlisle, Bradford, Rotherham, Rossendale, Warrington and West Lancashire in the North; Crawley and Southampton in the South East and Exeter in the South West.

Labour’s ambition in Scotland is to finish second, while in Wales it aims to limit any losses with the ambition of remaining in control of the Cardiff assembly.

However, a source close to Corbyn said the party was likely to lose control of the Welsh government, where it currently governs alone, and “not maintain our current position” in English councils.

“There are some people on the right of the party who are looking to promote unrealistic expectations. We will suffer some losses,” the source said.

Asked if they were now expecting a leadership challenge after the elections, he said: “Yes, I won’t deny it. But we are in a position to fend off attacks if and when they come.

“If there is a challenge we could organise a campaign by the weekend. We could set up phone banks tomorrow,” said the source. “During the last leadership election, when the others had phone banks of 15 people, we had 350.”

Bloodbath

As a case in point, POLITICO understands the Labour Party has received as many emails complaining about the outspoken MP John Mann attacking Ken Livingstone for being a “Nazi apologist” as it has from members voicing concern about anti-Semitism.

Moderate Labour MPs are also concerned about the impact any challenge could have on the EU referendum and many feel it would be better, instead, to unite around Sadiq Khan in London as a “pole of mainstream, sensible resistance” to gradually undermine Corbyn’s position.

The senior party source said: “If there’s an assassination attempt that fails there will be a bloodbath — villagers lined up against a wall and shot. Just let Jeremy fail on his own terms. Any leadership challenge is going to fail.”

The Corbyn ally, who spoke to POLITICO on the basis of anonymity, also dismissed growing speculation that the Labour leader could stand aside for from his right-hand-man John McDonnell.

“I can tell you John McDonnell will not challenge Jeremy Corbyn for the Labour leadership.”

He also insisted Corbyn has no plans to stand aside. “It is impossible to know the workings of people’s inner minds, but it seems to me that Jeremy thrives on quite a large proportion of the job. I don’t expect him to go voluntarily and I don’t expect him to be defeated.”

“At the end of the day, being in Europe is more important than the Labour leadership right now” — Shadow minister

On Tuesday Corbyn himself dismissed the speculation, insisting that “of course” he would stand again if he faced a leadership challenge.

Any challenge to Corbyn is likely to come after the referendum but before the September party conference, when MPs expect the leadership to attempt to change the party’s rule book to make it much harder to remove the leader.

However, there is still concern that Labour MPs will not be able to unite around a single candidate before striking.

“It feels pretty bleak,” one member of the shadow cabinet said. “We need to see how bad it is going to be on Thursday. We then have to decide what’s for the greater good. At the end of the day, being in Europe is more important than the Labour leadership right now.”

Ready to pounce

Even areas where Labour is expected to win — primarily in London, where Khan has pulled ahead of his Conservative rival Zac Goldsmith — MPs believe this is “despite Jeremy, not because of him.”

Conservative mayoral candidate Zac Goldsmith poses for a photograph with current mayor of London Boris Johnson | Ben Pruchnie/Getty Images

The Labour leader’s opponents are also concerned that the row over anti-Semitism could give Corbyn the excuse he needs to explain away poor results.

“What Ken [Livingstone] has done is give Jeremy cover,” said one MP from the Blairite faction, which favors the centrist line of former prime minister Tony Blair. “They will say it’s all being drummed up by the Blairites — the ‘Bitterites’ as they now say — and that’s why we lost.”

Aware of this danger, the moderates are holding their tongue to avoid being blamed for the expected defeats Thursday.

MPs know the Labour leader cannot be removed until the membership loses faith

“We don’t want to give the Corbynites succour. Jeremy and John [McDonnell] are ready to pounce on any sign of disloyalty, but they know we’ve managed to hold the line quite well. If we voiced our true feelings it would just strengthen the Corbynites,” said the Blairite MP.

But a source in Momentum, the grassroots organisations set up to defend Corbyn after his shock leadership election, dismissed the idea that the centrists in Labour had been restrained. “We have faced a series of full-frontal attacks and the membership are really pissed off with it,” said the source.

It is this battle of interpretation that will define the next six months of Corbyn’s leadership.

But whatever the result Thursday, MPs know the Labour leader cannot be removed until the membership loses faith — and there’s no sign of that happening yet.